Answer:
B. enfrente
Step-by-step explanation:
"Detrás" means "behind"
"Enfrente" Can mean "opposite" or "in front."
if you translate the sentence with "detrás," you get:
The sofa is behind the window.
This doesn't make sense. However, if you translate the sentence with "enfrente," you get:
The sofa is in front of the window.
This does make sense.
Thus, the answer is B. Enfrente
[I suggest using the website SpanishDict.com, it's very helpful.]